Field of the Invention
The present invention relates to an inkjet printer and a method of controlling inkjet printing, particularly to a control technique to reduce effects of noise from characteristics of printing paper sheets during various detections and printing corrections based on data optically read from printing results.
Description of the Related Art
Different types of printing paper sheets have different characteristics and give different printing results with the same amount of ink in the same conditions with an inkjet printer. Accordingly, to detect an ejection state or perform printing correction by optically reading the printing results, it is preferable to optimize the detection conditions or correcting operations depending on the type of the printing paper sheet. Examples of “detection” based on the read printing results include ejection failure detection to detect ejection failed nozzles, and printing defect detection to detect printing defects. Examples of “printing correction” include print density correction to achieve a predetermined print density, and print density unevenness correction to achieve printing without unevenness.
However, there are so many different types of printing paper sheets having different characteristics. Printing paper sheets having different thicknesses have different characteristics even if they are at the same grade. Besides, even at the same grade, printing paper sheets manufactured in different lots exhibit different characteristics as if they are of totally different types of printing paper sheets. This is because many types of printing paper sheets are mainly intended for use in offset printing or other conventional plate printing and not made suitable for printing with inkjet printers.
Accordingly, to perform higher quality of inkjet printing, it is effective to determine the conditions for optimizing detection or correction or prepare correction data for reading conducted for appropriate detection or correction, for individual printing paper sheets having different characteristics.
Since, however, so many types of printing paper sheets are in actual use, determination of the conditions for optimizing detection or correction or preparation of correction data for appropriate detection or correction for individual printing paper sheets complicates the process and increases the number of steps, and is therefore not a practical solution.
To solve this problem, Japanese Patent Laid-Open No. 2006-159602 proposes a method that provides preferred measurements in a measuring step of optically reading different types of printing paper sheets. The paragraph 0003 of Japanese Patent Laid-Open No. 2006-159602 says “it was found that the accuracy of correction of the density characteristics of the recording elements depends on the pattern or measured area recorded in a recording step, and the appropriate pattern or measured area varies depending on each recording media”. In addition, claim 2 of Japanese Patent Laid-Open No. 2006-159602 discloses “the data recorded in the recording step is changed according to the state of the surface of a recording medium”, and claim 4 of Japanese Patent Laid-Open No. 2006-159602 discloses “the area measured in the measuring step is changed according to the state of the surface of a recording medium”. It should be noted that “recording medium” in Japanese Patent Laid-Open No. 2006-159602 corresponds to “printing paper sheet” in this specification. “Recording” in Japanese Patent Laid-Open No. 2006-159602 corresponds to “printing” in this specification.